This invention concerns an improved process for melt spinning uniform polymeric filaments, especially in the form of heavy denier continuous filament polyamide yarns, by spinning at controlled withdrawal speeds.
There has also been increased interest in improving productivity of heavier denier, e.g. industrial, yarns via increased spinning speeds without sacrificing good yarn properties. Zimmerman in U.S. Pat. No. 3,091,015, which is incorporated herein by reference, discloses a process for spinning high tenacity industrial yarns at speeds of 440 ypm at the first feed roll to produce the desirable low birefringence yarns needed to obtain good mechanical yarn properties after the drawing steps. It would be very desirable from an economic viewpoint to provide an improved process which will remove the spinning speed limitations or raise the plateau which presently exists in the heavy denier industrial yarns without sacrificing good filament properties. However, an article by Professor A. Ziabicki in Fiber World, September 1984, pages 8-12, entitled "Physical Limits of Spinning Speed, questions whether higher speeds can yield fibers with better mechanical properties and whether there are any natural limits to spinning speed which cannot be overcome (concentrating on physical and material factors only and excluding economical and technical aspects of the problem). Professor Ziabicki concludes that there exists such a speed beyond which no further improvement of structure and fiber properties is to be expected. In the case of polyester textile filaments, the maxima appear to Professor Ziabicki to be around 5-7 km/min. For industrial yarns, although no such statement was made, no disclosure in the published literature was found which taught how to raise the spinning speed plateau for these yarns without loss of physical properties.
Accordingly, it was very surprising, according to the invention, to provide an improved process for obtaining polymeric filaments and yarns by spinning at significantly higher than conventional spinning speeds with similar or better mechanical properties than has been shown and predicted in the prior art for heavy denier yarns.